Perfluoroelastomers

ABSTRACT

Perfluoroelastomers curable by peroxidic way having glass transition temperature lower than −10° C. and an amount of —COF end groups in the polymer lower than the sensitivity limit of the method using the IR spectroscopy in Fourier transform described in the present application.

The present invention relates to perfluoroelastomers having a Tg (glasstransition temperature) lower than −10° C. and an improved combinationof mechanical and compression set properties in a wide range oftemperatures, at high and at low temperatures.

More specifically the present invention relates to perfluoroelastomershaving a Tg lower than −10° C. and substantially —COF end group free,said end groups being undetectable by the method indicated hereinafter.The perfluoroelastomers of the present invention show an improvedmolecular weight as shown by the improved intrinsic viscosity and areobtainable by a polymerization process with an improved productivity.

It is well known that perfluoroelastomers are polymers particularlyuseful in the aerospace, oil, petrochemical and semiconductor industrydue to their combination of thermal and chemical resistance and ofmaintenance of good mechanical and compression set properties. Howeverit is necessary that these polymers have an improved combination of theabove properties in a wide temperature range, at high and at lowtemperatures.

Various perfluoroelastomers have been suggested in the prior art toobtain the combination of the above properties, highly requested byperfluoroelastomer users. However in the prior art the —COF end groupvalues in perfluoroelastomers are not reported. The Applicant, afterdeep researches has found that, if the polymerization brings to polymershaving —COF end groups, the perfluoroelastomers do not show highmechanical and elastic properties.

Various perfluoroelastomers wherein the glass transition temperaturevalues are reported are known in the prior art. However in the prior artthe combination of a low Tg and of improved mechanical and elastomericproperties at high and at low temperatures is not obtained.

U.S. Pat. No. 3,132,123 describes the preparation ofperfluoroalkylvinylethers, their homopolymers and copolymers with TFE.The homopolymers are obtained under extreme experimental conditions, byusing polymerization pressures from 4,000 to 18,000 atm. The generalformula of the described vinylethers is the following:CF₂═CFOR⁰ _(F)wherein R⁰ _(F) is a perfluoroalkyl radical preferably from 1 to 5carbon atoms. Tests carried out by the Applicant have shown that thehomopolymer Tg is not very low and is of the order of −6° C.

U.S. Pat. No. 3,450,684 relates to vinylethers of formula:CF₂═CFO(CF₂CFX⁰O)_(n′)CF₂CF₂X⁰wherein X⁰=F, Cl, CF₃, H and n′ can range from 1 to 20. Also thehomopolymers obtained by UV polymerization are reported. The exemplifiedcopolymers are not characterized with their mechanical and elastomericproperties at low temperatures.

U.S. Pat. No. 3,635,926 relates to the emulsion copolymerization ofperfluorovinylethers with TFE. It is stressed that the presence of —COFend groups makes polymers unstable. The same was already reported inU.S. Pat. No. 3,085,083 in the polymerization systems ofperfluorovinyl-ethers in solvent.

U.S. Pat. No. 3,817,960 relates to the preparation and polymerization ofperfluorovinylethers of formula:CF₃O(CF₂O)_(n″)CF₂CF₂OCF═CF₂wherein n″ can range from 1 to 5. The vinylether synthesis is complex.No characterization data on the above properties are reported.

U.S. Pat. No. 3,896,179 relates to the separation of “primary”perfluorovinylether isomers, for example of CF₃CF₂CF₂OCF═CF₂ from therespective “secondary” less stable isomers CF₃(CF₃)CFOCF—═CF₂. Thelatter are undesired products as regards the polymer preparation and thepoor properties of the obtained polymers.

U.S. Pat. No. 4,487,903 refers to the preparation of fluoroelastomericcopolymers using perfluoro vinylethers of formula:CF₂═CF (OCF₂CFY⁰)_(n) ⁰OX²wherein n⁰ ranges from 1 to 4; Y⁰=F, Cl, CF₃, H; X² can be C₁-C₃perfluoroalkyl, C₁-C₃ ω-hydroperfluoroalkyl, C₁-C₃ω-chloroperfluoroalkyl. The polymer has a fluorovinylether unit contentranging from 15 to 50% by moles. Said vinylethers give copolymers havingat low temperatures properties higher than those of the above mentionedperfluorovinylethers PVE (perfluoropropylvinyl-ether) and MVE type. Inthis patent it is disclosed for having good properties at lowtemperature it is required the presence of at least two ether bonds inthe side chain adjacent to the double bond. Furthermore from the patentfor n⁰ values higher than 4 it is difficult to purify the monomers andthe effect on the T_(g) decrease is lower. Besides the reactivity of thedescribed vinylethers is very low and it is difficult to obtain polymershaving a high molecular weight capable to give good elastomericproperties for the mentioned applications. A TFE/perfluorovinylethercopolymer (n⁰=2) 31/69% by weight with Tg of −32° C. is exemplified.However the polymer is obtained with very long reaction times (96 hoursof polymerization). Also in this case no characterization data of thecured elastomer are given.

EP 130,052 describes the polymerization of perfluorovinylpolyethers(PVPE) which leads to amorphous perfluoropolymers having a T_(g) rangingfrom −15° to −100° C. In the patent copolymers and terpolymers of TFEand MVE with vinylethers (PVPE) of formula:CF₂═CFO(CF₂CF(CF₃)O)_(n′″)R⁰ _(f′)are described, wherein n′″ ranges from 3 to 30 and R⁰ _(f′) is aperfluoroalkyl. Owing to purification difficulties, the used vinylethersare vinylether mixtures with different n′″ values. According to thispatent the most marked effect on the T_(g) decrease is shown when n′″ isequal to or higher than 3, preferably higher than 4. According to thepolymerization examples described in said patent the final polymer mass,besides the hot and under vacuum treatment, must then be washed withfreon® TF to remove all the unreacteed monomer (PVPE). From the Exampleit can be seen that the reactivity of all the described monomers (PVPE)is poor.

U.S. Pat. No. 4,766,190 relates to the polymerization ofperfluorovinylpolyethers (PVPE) similar to those of U.S. Pat. No.4,487,903 with TFE and low perfluoropropene percentages, to increase themechanical properties of the obtained polymers.

U.S. Pat. No. 5,401,818 relates to the preparation ofperfluorovinylethers of formula:R¹ _(f)(OCF₂CF₂CF₂)_(m′)—OCF═CF₂(wherein R¹ _(f) is a C₁-C₃ perfluoroalkyl radical and m′ an integerranging from 1 to 4) and of the respective copolymers having improvedproperties at low temperature. The preparation of saidperfluorovinylethers takes place by 7 steps, of which some have very lowyields and comprising also a perfluorination with elemental F₂. Thereactivity of said perfluorovinylethers is anyway low.

Other problems shown by the prior art relate to the lowperfluorovinylether reactivity, making necessary the recovery from thereaction raw products of the unreacted monomers (British patent GB1,514,700), and the stability problems for the polymers having —C(O)Fend groups (U.S. Pat. No. 3,635,926). The latter can be furthertransformed with suitable reactants to increase the polymer stability(EP 178,935).

The perfluorooxyalkylvinylethers are furthermore used to givefluorinated rubbers good properties at low temperatures and inparticular to lower the glass transition temperature.

By increasing the perfluorooxyalkylene units, the Tg of the copolymersdecreases, but at the same time the vinylether reactivity drasticallydecreases, making difficult or impossible to obtain polymers having asufficiently high molecular weight to obtain polymers with goodproperties. Further the problems previously shown for the recovery ofthe unreacted monomer from the polymerization raw products or from thepolymer itself are still present (U.S. Pat. No. 4,487,903—EP 130,052).

The amorphous TFE copolymers with perfluoromethylvinylether having aT_(g) at about 0° C. or slightly lower (Maskornik, M. et al. “ECD-006Fluoroelastomer—A high performance engineering material”, Soc. PlastEng. Tech. Pao. (1974), 20, 675-7).

The extrapolated value of the T for the MVE homopolymer is about −5° C.(J. Macromol. Sci.-Phys., B1(4), 815-830, December 1967).

Other patents describing vinylethers for obtaining fluoroelastomers areknown. See U.S. Pat. No. 6,255,536 and WO 99/48,939.

Patent application EP 1,308,467 describes perfluoroelastomers containingfluoroalkoxyvinylethers of formula CFX_(A)═—CX_(A)OCF₂OR_(A), whereinX_(A)=F, H, R_(A) is C₂-C₆ perfluoroalkyl, perfluorooxyalkyl, or C₅-C₆cyclic (per)fluoroalkyl. In particular the followingperfluoroalkoxyvinylethers are described: CF₂═CFOCF₂OCF₂CF₃ (MOVE 1) andCF₂═CFOCF₂OCF₂CF₂OCF₃ (MOVE 2). In the Examples perfluoroelastomerscontaining at most about 40% of said perfluoroalkoxyvinylethers aredescribed. The MOVE perfluoroelastomers with TFE contain —COF endgroups. See the comparative Examples. To prepare polymeric compositionscontaining a TFE amount lower than or equal to 60% by moles it isnecessary to use long polymerization times. From the industrial point ofview this represent a drawback since the productivity is worsened.

Processes to remove or to reduce the —COF or other type of end groups inperfluoropolymers are described in the prior art. See for example patentapplication EP 1,256,591. The —COF end groups elimination, once thepolymer has been obtained, leads to certain application advantages, forexample when perfluorinated amorphous polymers are used for opticalapplications. However the mechanical properties do not improve afterthis treatment and therefore they do not solve the technical problemi.e. to have available perfluoroelastomers having an improvedcombination of mechanical and compression set properties in a widetemperature range, at high and at low temperatures.

The need was felt to have availabale perfluoroelastomers having thefollowing combination of properties:

-   -   Tg lower than −10° C., more preferably lower than −20° C., still        more preferably lower than −35° C., in particular lower than        −40° C.;    -   substantially —COF end group free, said end groups being        undetectable by the method indicated afterwards;    -   improved molecular weight, as shown by the higher value of the        intrinsic viscosity;    -   improved mechanical and compression set properties in a wide        temperature range, both at high and at low temperatures;    -   improved productivity of the process for obtaining        perfluoroelastomers, expressed as (polymer Kg)/(hour×liter of        water)

The Applicant has unespectedly and surprisingly foundperfluoroelastomers having a surprisingly improved combination of theabove mentioned properties.

It is an object of the present invention perfluoroelastomers curable byperoxidic route having a glass transition temperature lower than −10°C., preferably lower than −20° C., more preferably lower than −35° C.,in particular lower than −40° C., and having an amount of —COF end grouplower than the sensitivity limit of the method described herein: at theend of the polymerization, the polymer is isolated by coagulation byfreezing and subsequent defrosting; it is washed twice with demineralizdwater and is dried in a stove until a constant weight; the —COF endgroups are determined by FT-IR spectroscopy, wherein on a polymer filmhaving a thickness from 50 to 300 micron a scanning between 4000 cm⁻¹and 400 cm⁻¹ is carried out, the film being then kept for 12 hours in anenvironment saturated with ammonia vapours and recording the IR spectrumunder the same conditions of the initial IR spectrum; elaborating thetwo spectra by subtracting to the signals of the spectrum of theuntreated specimen (initial spectrum) the corresponding ones of thespecimen spectrum after exposure to ammonia vapours, drawing the“difference” spectrum, normalized by the following equation:

$\frac{``{{Difference}\mspace{14mu}{spectrum}}"}{\left\lbrack {{film}\mspace{14mu}{weight}\mspace{14mu}{(g)/{film}}\mspace{14mu}{area}\mspace{14mu}\left( {cm}^{2} \right)} \right\rbrack};$the optical densities related to the —COF end groups, reacted with theammonia vapours, are measured; the optical densities are converted intommoles/kg of polymer by using the extinction coefficients reported inTable 1, page 73 of the report by M. Pianca et Al. “End groups influoropolymers”, J. Fluorine Chem. 95 (1999), 71-84 (herein incorporatedby reference); the found values express the concentrations of theresidual —COF end groups as mmoles of end groups —COF/Kg of polymer: inthe perfluoroelastomer spectrum no bands related to COF groups(1900-1830 cm⁻¹) are detectable, the method sensitivity limit being 0.05mmoles/Kg.

More particularly the amountof of —COF end groups in the polymer isdetermined by using the Nicolet® Nexus FT-IR equipment (256 scannings,resolution 2 cm⁻¹).

The perfluoroelastomers according to the present invention preferablycomprise also units deriving from bis-olefins of general formula:

wherein:

-   -   R₁, R₂, R₃, R₄, R₅, R₆, equal to or different from each other,        are H or C₁-C₅ alkyls;    -   Z is a C₁-C₁₈ linear or branched alkylene or cycloalkylene        radical, optionally containing oxygen atoms, preferably at least        partially fluorinated, or a (per)fluoropolyoxyalkylene radical,        as described in EP 661,304 in the name of the Applicant.

The amount of bis-olefins is generally from 0.01 to 1.0% by moles,preferably from 0.03 to 0.5% by moles, still more preferably from 0.05to 0.2 moles per 100 moles of the above monomeric units, constitutingthe perfluoroelastomer structure; the monomer total sum being 100%.

In formula (I), Z is preferably a C₄-C₁₂, more preferably C₄-C₈,perfluoroalkylene radical, while R₁, R₂, R₃, R₄, R₅, R₆ are preferablyhydrogen;

-   when Z is a (per)fluoropolyoxyalkylene radical, it can comprise    units selected from the following:-   —CF₂CF₂C—, —CF₂CF(CF₃)O—, —CFX₁O— wherein X₁=F, CF₃, —CF₂CF₂CF₂O—,    —CF₂—CH₂CH₂O—, —C₃F₆O—.

Preferably Z has formula:-(Q)_(p)-CF₂O—(CF₂CF₂O)_(m)(CF₂O)_(n)—CF₂—(O)_(p)-  (II)wherein: Q is a C₁-C₁₀ alkylene or oxyalkylene radical; p is 0 or 1; mand n are numbers such that the m/n ratio is between 0.2 and 5 and themolecular weight of said (per)fluoropolyoxyalkylene radical is in therange 500-10,000, preferably 700-2,000.

Preferably Q is selected from:

-   —CH₂OCH₂—; —CH₂O(CH₂CH₂O)CH₂—, s being=1-3

The bis-olefins of formula (I) wherein Z is an alkylene or cycloalkyleneradical can be prepared according to what described, for example, by I.L. Knunyants et al. in Izv. Akad. Nauk. SSSR, Ser. Khim., 1964(2),384-6. The bis-olefins containing (per)fluoropolyoxyalkylene structuresare described in U.S. Pat. No. 3,810,874.

More preferably the bis-olefin has formula:CH₂═CH—(CF₂)_(t0)—CH═CH₂wherein t0 is an integer from 6 to 10.

The bis-olefin of formula:CH₂═CH—(CF₂)₆—CH═CH₂  (b).is particularly preferred.

The perfluoroelastomers of the invention are cured by peroxidic route.For this reason the invention curable perfluoroelastomers containpreferably iodine and/or bromine, more preferably iodine, in amountsgenerally between 0.001% and 5% by weight, preferably between 0.01% and2.5% by weight with respect to the total polymer weight. The iodineatoms can be present in the chain and/or in end position.

To introduce iodine and/or bromine atoms along the chain, thecopolymerization of the basic monomers of the fluoroelastomer is carriedout with a suitable fluorinated comonomer containing iodine and/orbromine (cure-site monomers), see for example U.S. Pat. Nos. 4,745,165,4,831,085, 4,214,060, EP 683,149. Said fluorinated comonomer containingiodine can be selected for example from the following compounds:

-   (a) iodo(per)fluoroalkyl-perfluorovinylethers of formula:    I−R_(f)—O—CF═CF₂  (III)-    wherein R_(f) is a C₁-C₁₂ (per)fluoroalkylene, optionally    containing chlorine and/or ether oxygen atoms; for example:    ICF₂—C—CF═CF₂, ICF₂CF₂—O—CF═CF₂, ICF₂CF₂CF—O—CF═CF₂,    CF₃CFICF₂—O—CF═CF₂, and the like;-   (b) iodo-(per)fluoroolefins of formula:    I—R′_(f)—CF═CF₂  (IV)-    wherein R′_(f) is a C₁-C₁₂ (per)fluoroalkylene, optionally    contining chlorine atoms; for example: iodotrifluoroethylene,    1-iodo-2,2-difluoroethylene,    iodo-3,3,4,4-tetrafluorobutene-1,4-iodo-perfluorobutene-1, and the    like;-   (c) iodo-(per)fluoroolefins of formula:    CHR_(O)═CH-Z_(O)-CH₂CHR_(O)—I  (V)-    wherein: R_(O) is H or —CH₃; Z_(O) is a C₁-C₁₈ linear or branched    (per)fluoroalkylene radical, optionally containing one or more    oxygen atoms, or a (per)fluoropolyoxyalkylene radical as above    defined.

Other cure-site iodinated comonomers are iodofluoroalkylvinylethers, seeU.S. Pat. Nos. 4,745,165 and 4,564,662.

Alternatively, or in addition to the iodinated comonomer, theperfluoroelastomer can contain iodine atoms in end position, derivingfrom a suitable iodinated chain transfer agent introduced in thereaction medium during the polymer preparation, as described in U.S.Pat. No. 4,501,869. Said transfer agents have formula R^(A) _(f)(I)_(x),wherein R^(A) _(f) is a C₁-C₁₂ (per)fluoroalkyl radical, optionallycontaining chlorine atoms, while x is 1 or 2. Said transfer agents canbe selected, for example, from: CF₂ —I₂, I(CF₂)₆I, I(CF₂)₄I, CF₂ClI,CF₃CFICF₂I, and the like.

For the iodine introduced as chain end group by addition of iodinatedchain transfer agents as above see for example U.S. Pat. Nos. 4,243,770and 4,943,622.

It is also possible to use as chain transfer agents alkaline oralkaline-earth metal iodides, according to patent application EP407,937.

In combination with the chain transfer agents containing iodine, otherknown chain transfer agents of the prior art can be used, as ethylacetate, diethylmalonate, etc.

The iodine amount in end position of the perfluoroelastomer is generallybetween 0.001% and 3%, preferably between 0.01% and 1% by weight withrespect to the fluoroelastomer weight. See U.S. Pat. Nos. 4,035,565 and4,694,045. Furthermore the curable perfluoroelastomers can contain,alternatively or in combination with iodine, also bromine, in the chainand in end position. The bromine in the chain can be introducedaccording to known techniques; see for example U.S. Pat. Nos. 4,035,565,4,745,165, EP 199,138; or as end bromine as described in U.S. Pat. No.4,501,869.

Preferably the perfluoroelastomer contains iodine atoms in the chainand/or in end position.

Optionally the invention perfluoroelastomers comprise in admixture asemicrystalline (per)fluoropolymer, in an amount in percent by weightreferred to the total of the dry weight of the mixtureperfluoroelastomer+semicrystalline (per)fluoropolymer, from 0% to 70%,preferably from 0% to 50% by weight, still more preferably from 2% to30% by weight.

With semicrystalline (per)fluoropolymer it is meant a (per)fluoropolymershowing, besides the glass transition temperature Tg, at least onecrystalline melting temperature.

The semicrystalline (per)fluoropolymer is constituted oftetrafluoroethylene (TFE) homopolymers, or TFE copolymers with one ormore monomers containing at least one unsaturation of ethylene type, inan amount from 0.01% to 10% by moles, preferably from 0.05% to 7% bymoles.

Said comonomers having an ethylene unsaturation are both of hydrogenatedand fluorinated type. Among those hydrogenated, ethylene, propylene,acrylic monomers, for example methylmethacrylate, (meth) acrylic acid,butylacrylate, hydroxyethylhexylacrylate, styrene monomers, can bementioned.

Among fluorinated comonomers it can be mentioned:

-   -   C₃-C₈ perfluoroolefins, as hexafluoropropene (HFP),        hexafluoroisobutene;    -   C₂-C₈ hydrogenated fluoroolefins, as vinyl fluoride (VF),        vinylidene fluoride (VDF), trifluoroethylene,        perfluoroalkylethylene CH₂═CH—R_(f), wherein R_(f) is a C₁-C₆        perfluoroalkyl;    -   C₂-C₈ chloro- and/or bromo- and/or iodo-fluoroolefins, as        chlorotrifluoroethylene (CTFE);    -   CF₂═CFOR_(f) (per)fluoroalkylvinylethers (PAVE), wherein R_(f)        is a C₁-C₆ (per)fluoroalkyl, for example CF₃, C₂F₅, C₃F₇;    -   CF₂═CFOX (per)fluoro-oxyalkylvinylethers, wherein X is: a C₁-C₁₂        alkyl, or a C₁-C₁₂ oxyalkyl, or a C₁-C₁₂ (per)fluoro-oxyalkyl        having one or more ether groups, for example        perfluoro-2-propoxy-propyl; fluorodioxoles, preferably        perfluorodioxoles.

PAVEs, in particular perfluoromethyl-, ethyl-, propylvinylether andfluorodioxoles, preferably perfluorodioxoles, are preferred comonomers.

When the perfluoroelastomers of the present invention containsemicrystalline (per)fluoropolymers, mixing is carried out by mixing inthe desired ratios the perfluoroelastomer latex with the semicrystallineperfluoropolymer latex and then co-coagulating the obtained mixture asdescribed in U.S. Pat. Nos. 6,395,834 and 6,310,142.

Alternatively the semicrystalline (per)fluoropolymer can be polymerizedand then the perfluoroelastomer is let polymerize on the(per)fluoropolymer particles. It is thus obtained a core-shellstructure.

The Applicant has found that when the —COF end group amount in theperfluoropolymer, after polymerization, is substantially absentaccording to the above analysis method, it is obtained the bestcombination of mechanical and compression set properties in a widetemperature range, both at high and at low temperatures.

It is a further object of the present invention compositions comprising:

-   -   perfluoroelastomers of the present invention, having an amount        of —COF end groups lower than 0.05 mmoles/Kg and Tg as above        defined, and    -   perfluoroelastomers obtainable from polymers containing an        amount of —COF end group higher than 0.05 mmoles/Kg;        provided that the amount of perfluoroelastomer of the present        invention is at least 5-10% by weight, preferably 20-40% by        weight, more preferably 50% by weight, with respect to the total        weight of the perfluoroelastomers in the composition.

These compositions can be obtained in various ways. For example, whenmonomers giving —COF end groups are used in polymerization to obtain theimproved properties according to the present invention it is carried outa part of polymerization of monomers in the absence of those giving —COFend groups, so as to obtain a polymer aliquot substantially —COF endgroup free which allows to obtain the combination of the aboveproperties. For example the polymer obtained in the polymerizat-ion partcarried out in the absence of monomers giving —COF end groups must be atleast 5-10% by weight, preferably 20-40% by weight, more preferably 50%by weight, with respect to the final polymer weight. An alternativeprocess is that to mix the polymers of the present inventionsubstantially —COF end group free with polymers containing —COF in theabove indicated ratios.

The perfluoroelastomers containing —COF end groups in an amount higherthan 0.05 mmoles/Kg comprise comonomers selected from the following:

-   -   perfluorodioxoles, preferably having the following formula:

-   -   wherein    -   Y═F, ORf₁, Rf₁ being a C₁-C₅ perfluoroalkyl, preferably Rf₁ is        CF₃;    -   X₁ and X₂, equal to or different from each other, are selected        between F and CF₃, preferably F;    -   Z₁ is selected between F, Cl, preferably F;    -   perfluoroalkylvinylethers of formula CF₂═CFORf wherein Rf is a        C₃ perfluoroalkyl;    -   CF₂═CFOXa perfluorooxyalkylvinylethers, wherein Xa is C₃-C₁₂        perfluorooxyalkyl having one or more ether groups, for example        perfluoro-2-propoxy-propyl;    -   perfluorovinylethers (MOVE) of general formula        CFX_(AI)═CX_(AI)OCF₂OR_(AI) (A-I) wherein R_(AI) is a C₂-C₆        linear, branched or C₅-C₆ cyclic perfluoroalkyl group, or a        C₂-C₆ linear or branched when possible perfluorooxyalkyl group        containing from one to three oxygen atoms; X_(AI)=F; the        compounds of general formula: CFX_(AI)═CX_(AI)OCF₂OCF₂CF₂Y_(AI)        (A-II) wherein Y_(AI)=F, OCF₃ are preferred; in particular        (MOVE 1) CF₂═CFOCF₂OCF₂CF₃ (A-III) and (MOVE 2)        CF₂═CFOCF₂OCF₂CF₂OCF₃ (A-IV).

The curable perfluoroelastomers of the invention preferably comprise thefollowing monomers (percent by moles):

-   A) from 1% to 100%, preferably from 5% to 100%, of the monomer of    formula:    CF₂═CFOCF₂OCF₃  (a)-   B) one or more perfluorinated comonomers having at least one    ethylene type unsaturation, from 0% to 99%, preferably from 0 to    95%;    the sum of the molar monomer percentages being 100%; with the    proviso that when comonomer B) is TFE or the mixture of    comonomers B) contains TFE, the TFE amount must be such that the    polymer is elastomeric; the —COF end groups amount being as above.

Said perfluoroelastomers preferably contain one bis-olefin.

More particularly the amount of —COF end groups in the polymer isdetermined by using the Nicolet® Nexus FT-IR apparatus (256 scannings,resolution 2 cm⁻¹).

Elastomeric polymers, according to the present invention are polymerswhich at the DSC (differential scanning calorimetry) do not show meltingpeaks, since the crystalline part is substantially absent.

When the copolymer does not contain other comonomers (B) besides TFE,the monomer amount of formula (a) is generally higher than about 15% bymoles to obtain elastomeric polymers.

Comonomers B) are selected from the following:

-   -   C₂-C₈ perfluoroolefins, for example TFE, hexafluoropropene;    -   perfluoroalkylvinylethers of formula CF₂═CFORf wherein Rf is a        C₁-C₂ perfluoroalkyl, preferably Rf=CF₃.

Tetrafluoroethylene (TFE) and/or perfluoromethylvinylether (MVE) arepreferred comonomers B).

Preferred compositions (in % by moles) are the following, the sum of themonomer molar percentages being 100%; more preferably said compositionscontain a bis-olefin:

-   monomer of formula (a): 100%;-   preferably monomer of formula (a): 99.0%-99.99% bis-olefin of    formula (b) 1%-0.01%; more preferably monomer of formula (a):    99.90-99.99%, bis-olefin of formula (b) 0.1-0.01%;-   monomer of formula (a): 15-40%, TFE: 60-85%; preferably monomer of    formula (a): 18-30%, TFE: 69-81.99%, bis-olefin of formula (b)    1-0.01%;-   monomer of formula (a): 40-99%, TFE: 1-60%; preferably monomer of    formula (a): 39-98.99%, TFE 1-60%, bis-olefin of formula (b)    1-0.01%;-   monomer of formula (a): 5-40%, MVE: 5-30%, TFE: 50-85%; preferably    monomer of formula (a): 5-40%, MVE: 5-30%, TFE: 50-85%, bis-olefin    of formula (b) 1-0.01%;-   monomer of formula (a): 40-99%, MVE: 5-30%, TFE: 1-60%; preferably    monomer of formula (a): 40-99%, MVE: 5-30%, TFE: 1-60%, bis-olefin    of formula (b) 1-0.01%.

As said, the perfluoroelastomers of the invention show an improvedcombination of the above properties.

The perfluoroelastomers of the present invention show a good elasticbehaviour at low temperatures, as for example shown by the TR10 and TR70values (ASTM D 1329).

The perfluoroelastomers of the present invention compared with theperfluoroelastomers of the prior art having a Tg lower than −10° C., thecomparison being carried out with the same Tg, show improved mechanicaland compression set properties and a higher resistance at hightemperatures. In a comparison carried out with theperfluoromethylvinylether based perfluoroelastomers (the most largelymarketed perfluoroelastomers) the perfluoroelastomers of the presentinvention show a lower Tg and improved properties at low temperatures,as shown by the TR values.

The Applicant has unexpectedly and surprisingly found that theperfluoroelastomers of the present invention are obtained with highpolymerization kinetics, therefore it is possible to obtain homopolymersand copolymers having a high molecular weight. The perfluoroelastomersof the present invention are obtainable with high yields and thereforethe recovery of the unreacted monomers is useless, at the end of thepolymerization. This allows to simplify the production plant, since theexpensive recovery methods of unreacted monomers are not necessary.

The preparation of perfluoroelastomers of the present invention iscarried out by polymerization of the monomers in aqueous emulsion in thepresence of an emulsion, dispersion or microemulsion ofperfluoropolyoxyalkylenes, according to U.S. Pat. Nos. 4,789,717 and4,864,006. Preferably the synthesis is carried out in the presence of aperfluoropolyoxyalkylene microemulsion.

According to well known methods of the prior art, radical initiators,for example alkaline or ammonium persulphates, perphosphates, perboratesor percarbonates, optionally in combination with ferrous, cupreous orsilver salts, or other easily oxidizable metals, are used. In thereaction medium also surfactants of various kind are optionally present,among which fluorinated surfactants of formula:R³ _(f)—X_(k) ⁻M⁺are particularly preferred, wherein R³ _(f) is a C₅-C₁₆ (per)fluoroalkylchain or (per)fluoropolyoxyalkyl chain, X_(k) ⁻ is —COO⁻ or —SO₃ ⁻, M⁺is selected among: H⁺, NH₄ ⁺, or an alkaline metal ion. Among the mostcommonly used we remember: ammonium perfluorooctanoate,(per)fluoropolyoxyalkylenes ended with one or more carboxylic groups,etc. See U.S. Pat. Nos. 4,990,283 and 4,864,006.

The polymerization reaction is generally carried out at temperaturesbetween 25° C. and 150° C., at a pressure between the atmosphericpressure up to 10 MPa.

In alternative or in combination with the chain transfer agentscontaining iodine and/or bromine, other chain transfer agents known inthe prior art, as ethyl acetate, diethylhylmalonate, ethane, etc., canbe used.

As said, the perfluoroelastomers of the present invention are cured byperoxidic route.

In the peroxidic curing, preferably the perfluoroelastomer contains inthe chain and/or in end position to the macromolecule iodine and/orbromine atoms.

To the curing blend the following components are added:

-   -   peroxides capable to generate radicals by heating, for example:        dialkylperoxides, in particular di-terbutyl-peroxide and        2,5-dimethyl-2,5-di(terbutylperoxy)hexane; dialkylarylperoxides        as for example dicumyl peroxide; dibenzoyl peroxide; diterbutyl        perbenzoate; di[1,3-dimethyl-3-(terbutylperoxy)butyl]-carbonate.        Other peroxidic systems are described, for example, in European        patent applications EP 136,596 and EP 410,351.

The peroxide amount is generally from 0.5% to 10% by weight with respectto the polymer, preferably 0.6%-4% by weight;

-   -   curing coagents, in amounts generally between 0.5 and 10%,        preferably between 1 and 7%, by weight with respect to the        polymer; among them, bis-olefins of formula (I);        triallyl-cyanurate, triallyl-isocyanurate (TAIC),        tris(diallylamine)-s-triazine; triallylphos-phite;        N,N-diallyl-acrylamide; N,N,N′,N′-tetraallyl-malonamide;        tri-vinyl-isocyanurate; and 4,6-tri-vinyl-methyltrisiloxane,        etc., are commonly used: TAIC and the bis-olefin of formula        CH₂═CH—(CF₂)₆—CH═CH₂;    -   are particularly preferred; optionally    -   a metal compound, in amounts between 1 and 15%, preferably from        2 to 10% by weight with respect to the polymer, selected from        divalent metal oxides or hydroxides, as for example Mg, Zn, Ca        or Pb, optionally combined with a weak acid salt, as stearates,        benzoates, carbonates, oxalates or phosphites of Ba, Na, K, Pb,        Ca;    -   other conventional aditives, as mineral fillers, semicrystalline        fluoropolymers in powder, pigments, antioxidants, stabilizers        and the like.

The semicrystalline (per)fluoropolymers, optional components of thepresent invention, are prepared according to the emulsion ormicroemulsion polymerization methods above described for theperfluoroelastomers of the invention.

The monomer of formula (a) CF₃OCF₂OCF═CF₂ used in the polymers of thepresent invention can be prepared by a synthesis comprising thefollowing steps:

-   I obtainment of the fluoroformate CF₃OCOF;-   II reaction in liquid phase of the fluoroformate CF₃OCOF with    elemental fluorine and olefinic compounds having formula:    CAF═CA′F  (IV)    -   for obtaining the fluorohalogenether of formula:        CF₃OCF₂OCFACF₂A′  (V)    -   wherein A and A′, equal to or different the one from the other,        are H, Cl or Br, with the proviso that both are not H; the        fluorination reaction temperture can range from −120° C. to −20°        C., preferably from −100° C. to −40° C.;    -   optionally one operates in the presence of a perhalogenated        solvent, liquid and inert under the reaction conditions; the        fluorine can optionally be diluted with an inert gas, e.g.        nitrogen or helium;-   III removal of the substituents A and A′ from the    fluorohalogenether (V) by a dehalogenation when A and A′ are    halogen, or a dehydrohalogenation when one of A or A′ is hydrogen    and the other is halogen;    the fluoroformate CF₃OCOF of step I can be prepared with high    conversion and selectivity by thermal reaction, in gaseous phase, of    CF₃OF (fluoroxyperfluoromethane) with CO in a reactor maintained at    temperatures between 80° C. and 250° C., preferably between 120° C.    and 230° C., still more preferably between 150° C. and 200° C.

The dehalogenation or dehydrohalogenation reactions used are well knownin the prior art.

The molar ratio CF₃OF/CO is between 0.1 and 10, preferably between 0.2and 5, more preferably between 0.5 and 2.

The perhalogenated solvent optionally used in step II, is preferably anorganic compound containing fluorine and/or chlorine, optionally one ormore oxygen atoms in the chain and/or aminic groups as the end group.

When the perhalogenated solvent is perfluorinated, it can for example beselected among perfluorocarbons, perfluoroethers, perfluoropolyethers,perfluoroamines, or respective mixtures.

The reaction mixture containing CF₃OCOF of step I can be directly fed,without separation of the mixture components, into the other reactor forthe reaction of step II. The process for obtaining the monomer of step Istarting from CF₃OF resulted particularly simple and effective. As said,the CF₃OF conversion and the selectivity to CF₃OCOF are high (see theExamples).

In step I, by increasing the reaction temperature in the range 80°-250°C., the conversion increases and, at the same time, a high selectivityis substantially maintained.

Alternatively, the CF₃OCOF of step I can be prepared by photochemicalroute, in liquid phase, by feeding the two reactants, as aboveindicated, into a reactor equipped with a mercury high pressure UV lamp,contained in a cooled quartz sheath, immersed in the reaction mixture,at temperatures comprised between 0° C. and 100° C., preferably between20° C. and 50° C.,

It has been found that the formation reaction of the fluoroformate byphotochemical route has a high selectivity, and that higher yields areobtained compared with the same reaction carried out in gaseous phase.

The reaction by photochemical route is carried out in the presence of aninert perfluorinated solvent, liquid under the reaction conditions.

Preferably the perfluorinated solvent is selected from perfluorocarbons,perfluoropolyethers, perfluorinated tertiary amines,fluorochlorocarbons, or mixtures thereof.

When the CF₃OF conversion is not quantitative, the gaseous flow leavingthe reactor contains a mixture formed of the reaction product togetherwith unconverted CO and CF₃OF. The latter can be removed by passing thegaseous flow into a cold trap containing a fluorinated olefin, forexample CFCl═CFCl; then by fractional distillation CF₃OCOF is separated.

Alternatively the gaseous reaction mixture containing the reactionproducts formed in step I is cooled to condensate the fluoroformateseparating CF₃OF and CO which can be recycled into the reactor.

Preferably step I is carried out by reacting thefluorooxyperfluoromethane and carbon monoxide at temperatures from 80°C. to 250° C.

Preferably the reactor used in step I is made of glass, inertperfluorinated plastics, as for example PTFE, PFA, metal alloys, forexample AISI 316, preferably coated with glass or perlfuorinatedplastics. More preferably, as materials, glass or fluorinated plasticsare used.

The perfluoroelastomers of the present invention, as said, show animproved combination at high temperatures of mechanical properties, inparticular modulus, stress at break and elongation at break, ofelastomeric properties as shown by the compression set, and of thermalresistance; and contemporaneously they show an improved combination ofthe above properties even at low temperatures.

The perfluoroelastomers of the present invention are usable to obtainmanufactured articles for temperatures lower than −10° C. up to 300° C.,having improved mechanical and elastomeric properties.

The following Examples illustrate with non limitative purposes thepresent invention.

EXAMPLES

Analytical Methods

Determination of the Polymer Tg

The Tg has been determined by DSC analysis according to the ASTM D 3418method. The Tg values reported in the Examples are the mid-point Tg.

Determination of the Intrinsic Viscosity

The intrinsic viscosity has been determined in perfluoroheptane at thetemperature of 30° C.

Determination of the —COF Polar End Groups

At the end of the polymerization, the polymer is isolated by coagulationby freezing at −20° C. and subsequent defrosting at room temperatureuntil obtaining a slurry wherein the polimer deposits on the bottom; itis washed twice with demineralized water and it is dried in a stove at90° C. until a constant weight (about 12 hours); the —COF end groups aredetermined by FT-IR spectroscopy, by using the Nicolet® Nexus FT-IRequipment (256 scannings, resolution 2 cm⁻¹), wherein on a polymer filmhaving a thickness from 50 to 300 micron a scanning between 4000 cm⁻¹and 400 cm⁻¹ is initially carried out, the film being then kept for 12hours in an environment saturated with ammonia vapours, and recording atthe end the IR spectrum under the same conditions of the initial IRspectrum; elaborating the two spectra by subtracting to the signals ofthe spectrum related to the untreated specimen (initial spectrum) thecorresponding signals of the specimen spectrum after exposure to ammoniavapours, drawing the “difference” spectrum, normalized by the followingequation:

$\frac{``{{Difference}\mspace{14mu}{spectrum}}"}{\left\lbrack {{film}\mspace{14mu}{weight}\mspace{14mu}{(g)/{film}}\mspace{14mu}{area}\mspace{14mu}\left( {cm}^{2} \right)} \right\rbrack};$the optical densities related to the —COF end groups, reacted with theammonia vapours, are measured; the optical densities are converted intommoles/kg of polymer by using the molar extinction coefficient of the—COF group at 1884 cm⁻¹, equal to 215 liters/(moles×cm), as reported inTable 1, page 73 of the report by M. Pianca et Al. “End groups influoropolymers”, J. Fluorine Chem. 95 (1999), 71-84 (herein incorporatedby reference); the found values express the concentrations of theresidual —COF end groups as mmoles of end groups —COF/Kg of polymer: inthe perfluoroelastomer spectrum no bands related to COF groups(1900-1830 cm⁻¹) are detectable, the method sensitivity limit being 0.05mmoles/Kg.Mooney Viscosity Determination

The Mooney viscosity (1+10′ at 121° C.) is determined according to theASTM D 1646 method.

Compression Set Determination

The Compression Set is determined according to the ASTM D 395 method.

TR Determination

The TR Test is determined according to the ASTM D 1329 method.

Example A

Preparation of CF₃OCOF by Thermal Reaction at 170° C. in Glass Reactor

A tubular glass reactor is used, having an inner diameter of 55.6 mm andlength of 510 mm, filled with 6×6 glass Raschig rings (free internalvolume 842 ml), maintained thermostated by electric resistances.

In the reactor, maintained at the temperature of 170° C., a gaseous flowof CF₃OF (1.5 liters/hour), synthesized as described in U.S. Pat. No.4,400,872 and, contemporaneously, a CO flow (1.5 liters/hour), are fedfor 5 hours. The flow coming out from the reactor is continuouslyanalyzed by online gaschromatographic analysis.

The flow coming out from the reactor is condensed, except CO, in a trapmaintained at −110° C. containing 15 g of CFCl=CFCl (A 1112), so thatthe residual CF₃OF reacts with the olefin to give CF₃OCFClCF₂Cl.

After fractional distillation of the resulting mixture, 33.9 g ofCF₃OCOF pure at 99.8% (molar yield on the fed CF₃OF 76.5%); 12.3 g ofCF₃OCFClCF₂Cl; 3.4 g of COF₂ are obtained.

The conversion is 84.5% and the selectivity 90%, calculated on the fedCF₃OF.

Example B

Preparation of CF₃OCOF by Thermal Reaction at 170° C. in PTFE Reactor

A PTFE tubular thermostated reactor is used, having an internal diameterof 4 mm and length of 13.2 m.

A gaseous flow of CF₃OF (1.5 liters/hour) and, contemporaneously, a flowof CO (2.0 liters/hour) are fed into the reactor, maintained at thetemperature of 170° C.

The flow coming out from the reactor, analyzed by gaschromatography, hasthe following molar composition: 7.3% CF₃OF, 54.2% CF₃OCOF, 9.1% COF₂and 29.4% CO.

Example C

Preparation of CF₃OCOF by Thermal Reaction at 120° C. in PTFE Reactor

A gaseous flow of CF₃OF (1.5 liters/hour) and, contemporaneously, a flowof CO (2.0 liters/hour) are fed for 6 hours into the same reactor usedin the Example B, maintained at the temperature of 120° C. The flowcoming out from the reactor is analyzed by gaschromatography and has thefollowing molar composition, leaving out CO in excess: 86.7% CF₃OF,13.3% CF₃OCOF.

The flow coming out from the reactor is condensed, except CO, in a trapmaintained at −110° C. containing 50 g of A 1112, so that the residualCF₃OF reacts with the olefin.

After fractional distillation of the resulting mixture, 6.8 g of CF₃OCOFhaving a 99% purity are obtained.

The selectivity is 98%, calculated on the converted CF₃OF The conversionis 13.0%.

Example D

Preparation of CF₃OCOF by Thermal Reaction at 170° C. in AISI 316Reactor

An AISI 316 tubular thermostated reactor is used, having an internaldiameter of 4 mm and length of 11.3 m.

A gaseous flow of CF₃OF (1.5 liters/hour) and, contemporaneously, a flowof CO (1.5 liters/hour) are fed for 6 hours into the reactor, maintainedat the temperature of 170-° C. The gaseous flow coming out from thereactor is condensed in a trap maintained at −110° C. containing 30 g ofA 1112.

After fractional distillation of the trap content, 31.2 g of CF₃OCOFpure at 99%, 31.8 g of fluorohalogenether and 3.7 g of COF₂ areobtained. The conversion is 66.6% and the selectivity is 86.5%.

Example E

Preparation of CF₃OCOF by Photochemical Reaction

500 g of a perfluoropolyether Galden® LS-165 are fed into a 300 mlcylindrical glass reactor, equipped with stirrer and UV lamp Hanau TQ150, with 150 W power and optical route 1 cm. Then 2.0 liters/hour ofCF₃OF diluted with 3.0 liters/hour of He, and 2.0 liters/hour of CO arefed contemporaneously for 5 hours.

The gases coming out from the reactor are condensed in a trap maintainedat −110° C. containing 30 g of A 1112. After fractional distillation ofthe condensed mixture, 22.9 g of CF₃OCOF pure at 99%, 41.8 g offluorohalogenether CF₃OCFClCF₂—Cl, 5.8 g of COF₂, 5.4 g oftrifluoromethyl carbonate are obtained.

The CF₃OF conversion is 60.5%. The selectivity is 63.6%.

Example F

Obtainment of the Monomer of Formula (a) by Reaction of CF₃O—COF withElemental Fluorine and a Fluoroolefin of Formula CFCl=CFCl andSubsequent Dehalogenation of the Fluorohalogenether

20 g of CFCl=CFCl (A 1112), 30 g of CF₃OCOF obtained as in the Example Aare transferred in a 50 ml glass reactor. The solution formed ismaintained at −100° C. and fluorine diluted with nitrogen is bubbled ata flow of 1 liter/hour.

The mass balance at the end of the reaction is 92%, the ¹⁹F-NMR analysison the reaction raw product (52 g) shows that the fluoroformateconversion is 54% and the selectivity to give the fluorohalogenetherCF₃OCF₂OCFClCF₂Cl is 93%. The unreacted fluoroformate is removed fromthe reaction raw product by adding water, under stirring. It is letreach 25° C., the organic phase is recovered and dried over MgSO₄. Themixture is filtered and the obtained residue is distilled and thefraction boiling at 74° C. of 31.8 g corresponding to thefluorohalogenether having 99% purity is recovered.

The fluorohalogenether dehalogenation is carried out by using an 1 literflask equipped with mechanical stirrer, thermometer, funnel dropping,distillation column and trap at −78° C. 450 ml of dimethylformamide(DMF), 62 g of zinc in powder and 8.3 g of ZnCl₂ are fed into the flask.The temperature in the suspension is brought to 80° C. and 150 g of thefluorohalogenether isolated in the previous reaction are added. When theaddition is over, the mixture is let react for one hour. At the end thetemperature is gradually increased up to 120° C. and it is let reactstill for one hour. Lastly it is disconnected and 106 g of the monomerof formula (a) CF₃OCF₂OCF═CF₂ having 99% purity (boiling point 23° C.)are recovered therefrom.

Example 1

Preparation of the Microemulsion

The microemulsion is obtained by mixing the following ingredients in theamounts indicated hereinafter to prepare one liter of microemulsion:

-   -   220.7 ml of a perfluoropolyoxyalkylene having acid end group        with average molecular weight 600, of formula:        CF₂ClO(CF₂—CF (CF₃)°)_(n)(CF₂O)_(m)CF₂COOH    -    wherein n/m=10;    -   220.7 ml of an aqueous solution of NH₃ at 30% by volume;    -   427.6 ml of demineralized water;    -   131 ml of Galden® D02, having average molecular weight 450, of        formula:        CF₃O(CF₂—CF (CF₃)O)_(n)(CF₂O)_(m)CF₃    -    wherein n/m=20.

Example 2

Homopolymer of the Monomer of Formula (a)

0.03 l of demineralized water, 1.5 ml of the microemulsion of theExample 1, and 12 g of the monomer of formula (a) are introduced insequence into a 0.1 l (liters) glass autoclave, equipped with magneticstirring, after vacuum has been made by oil pump. The autoclave isheated to 42° C. Then 0.1 g of ammonium persulphate are introduced. Thereactor is maintained at 42° C. for 170 h and then cooled. The obtainedlatex is degassed. The latex is coagulated by freezing and subsequentdefrosting. In this way the polymer is separated from the aqueous phase;it is washed twice with demineralized water and dried in a stove at 100°C. for 8 h.

About 11 g of polymer equal to a conversion of 92% of the fed monomer offormula (a) are obtained. The polymer Tg is −39.4° C. The intrinsicviscosity measured at 30° C. in perfluoroheptane (Galden® D80) is equalto 30.5 cc/g. By IR analysis it is found that the —COF end groups in thepolymer are lower than the method sensitivity limit.

Conversions of about 69% of the monomer of formula (a) are obtained withlower polymerization times.

Example 3

Copolymer Monomer of formula (a)/TFE 63/37 (% by Moles Ratio)

20 ml of demineralized water, 1 ml of microemulsion prepared in theExample 1 are introduced in sequence into a 42 ml steel autoclave,equipped with magnetic stirring, after vacuum has been made by oil pump.10 g of the monomer of formula (a) are added and the autoclave is heatedto 80° C. TFE is introduced into the reactor until bringing the pressureto 1.0 MPa. Then 4 mg of ammonium persulphate are introduced. Thereaction pressure is maintained constant by addition of TFE at everypressure decrease equal to 0.01 MPa.

The reaction ends after 4 h. The obtained latex is degassed. The latexis coagulated by freezing and subsequent defrosting. In this way thepolymer is separated from the aqueous phase; it is washed twice withdemineralized water and dried in a stove at 90° C. for 4 h. 5.3 g ofpolymer equal to 43% of the fed monomer of formula (a) are obtained. Thepolymer Tg is −42.5° C. (midpoint) and −48.4° C. (onset). The intrinsicviscosity measured at 30° C. in perfluoroheptane (Galden® D80) is equalto 17.0 cc/g.

By NMR analysis the polymer composition is determined; it contains 63%by moles of the monomer of formula (a). By IR analysis it is found thatthe —COF end groups in the polymer are lower than the method sensitivitylimit.

Example 4 (Comparative)

Copolymer MOVE 1/TFE 23/77 (% by Moles Ratio)

20 ml of demineralized water, 1 ml of microemulsion prepared in theExample 1 are introduced in sequence into a 42 ml steel autoclave,equipped with magnetic stirring, after vacuum has been made by oil pump.10 g of MOVE 1 are added and the autoclave is heated to 80° C. TFE isintroduced into the reactor until bringing the pressure to 1.0 MPa. Then4 mg of ammonium persulphate are introduced. The reaction pressure ismaintained constant by addition of TFE at every pressure decrease equalto 0.01 MPa.

The reaction ends after 4 h. The obtained latex is degassed. The latexis coagulated by freezing and subsequent defrosting. In this way thepolymer is separated from the aqueous phase; it is washed twice withdemineralized water and dried in a stove at 90° C. for 4 h. 4.0 g ofpolymer with a conversion of 18% of MOVE 1 with respect to the fedamount are obtained. The polymer Tg is −21.0° C. (midpoint) and −31° C.(onset).

By NMR analysis it is determined the polymer composition which contains23% by moles of MOVE 1. By IR analysis it is determined a —COF end groupcontent in the polymer equal to 0.25 mmoles/kg.

Example 5

Copolymer Monomer of Formula (a)/HFP

20 ml of demineralized water, 1 ml of microemulsion prepared in theExample 1 are introduced in sequence into a 42 ml steel autoclave,equipped with magnetic stirring, after vacuum has been made by oil pump.9 g of the monomer of formula (a) are added and the autoclave is heatedto 80° C. HFP is introduced into the reactor until bringing the pressureto 1.5 MPa. Then 4 mg of ammonium persulphate are introduced. Thereaction pressure is maintained constant by addition of HFP at everypressure decrease equal to 0.01 MPa.

The reaction ends after 4 h. The obtained latex is degassed. The latexis coagulated by freezing and subsequent defrosting. In this way thepolymer is separated from the aqueous phase; it is washed twice withdemineralized water and dried in a stove at 90° C. for 4 h. 0.5 g ofpolymer are obtained.

The IR analysis confirms that the obtained polymer is a copolymer basedon the monomer of formula (a) with a small amount of HFP (<5% by moles).

Example 6 (Comparative)

Copolymer MOVE 1/HFP

20 ml of demineralized water, 1 ml of microemulsion prepared in theExample 1 are introduced in sequence into a 42 ml steel autoclave,equipped with magnetic stirring, after vacuum has been made by oil pump.9 g of MOVE 1 are added and the autoclave is heated to 80° C. HFP isintroduced into the reactor until bringing the pressure to 1.5 MPa. Then4 mg of ammonium persulphate are introduced.

The reaction ends after 4 h. The reactor content is degassed and thencoagulation is carried out by freezing and subsequent defrosting. Nopolymer presence is observed. Then MOVE 1 in the adopted conditions isnot capable to copolymerize with HFP.

Example 7 (Comparative)

Homopolymer MOVE 1

0.03 l of demineralized water, 1.5 ml of microemulsion of the Example 1and 9 g of MOVE 1 are introduced in sequence into a 0.1 l (liters) glassautoclave, equipped with magnetic stirring, after vacuum has been madeby oil pump. The autoclave is heated to 42° C. Then 0.1 g of ammoniumpersulphate are introduced. The reaction is maintained at 42° C. for 170h and then it is cooled.

The obtained latex is degassed. The latex is coagulated by freezing andsubsequent defrosting. In this way the polymer is separated from theaqueous phase; it is washed twice with demineralized water and dried ina stove at 100° C. for 8 h.

About 6.2 g of polymer equal to a conversion of 69% of fed MOVE 1 areobtained. The polymer Tg is −31.6° C. The intrinsic viscosity measuredat 30° C. in perfluoroheptane (Galden® D80) is equal to 16.5 cc/g. By IRanalysis it is found that the —COF end groups in the polymer are 0.35mmoles/kg.

Example 8

Copolymer Monomer of formula (a)/TFE 64/36 (% by Moles Ratio) ContainingBis-olefin

20 ml of demineralized water, 1 ml of microemulsion prepared in theExample 1 are introduced in sequence into a 42 ml steel autoclave,equipped with magnetic stirring, after vacuum has been made by oil pump.10 g of the monomer of formula (a) are added and the autoclave is heatedto 80° C. 0.01 g of bis-olefin of formula CH₂═CH—(CF₂)₆—CH═CH₂ dissolvedin 0.1 g of Galden D02 are introduced and the pressure in the reactor isbrought to 1.0 MPa with TFE. Then 4 mg of ammonium persulphate areintroduced. The reaction pressure is maintained constant by addition ofTFE at every pressure decrease equal to 0.01 MPa.

The reaction ends after 4 h. The obtained latex is degassed. The latexis coagulated by freezing and subsequent defrosting. In this way thepolymer is separated from the aqueous phase; it is washed twice withdemineralized water and dried in a stove at 90° C. for 4 h. 5.5 g ofpolymer equal to 45% of the fed monomer of formula (a) are obtained. Thepolymer Tg is −44.0° C. (midpoint) and −50.0° C. (onset). The intrinsicviscosity, measured at 30° C. in perfluoroheptane (Galden® D80) is equalto 45.0 cc/g.

By NMR analysis the polymer composition is determined; it contains 64%by moles of the monomer of formula (a). By IR analysis it is found thatthe —COF end groups in the polymer are lower than the method sensitivitylimit.

Comments to Examples 23, 5 and 8 According to the Invention and to theComparative Examples 4, 6 and 7

The homopolymer of monomer (a) (example 2) over the homopolymer of MOVE1 (example 7 comparative) shows the following improved properties:

-   -   an higher intrinsic viscosity, therefore an higher molecular        weight;    -   absence of —COF end groups;    -   a lower Tg.

In the polymerization with other comonomer(s), monomer (a) shows a muchhigher reactivity than MOVE 1. Under similar polymerization conditionsand using TFE as comonomer, in example 3 it is obtained a polymercontaining 63% moles of monomer (a), in comparative example 4 thecontent of MOVE 1 in the copolymer is 23% moles. Under similarpolymerization conditions and using HFP as comonomer (see example 5) acopolymer of monomer (a) wherein the content of HFP is <5% moles wasobtained, in comparative example 6 the copolymer was not even formed.

The peculiar properties of the copolymers containing monomer (a) arealso shown by the Tg values. The copolymers of monomer (a) and TFE ofexamples 3 and 8, show a Tg of 42.5° C. and 44.0° C. respectively. Itmust be noted that these Tg values are lower than the Tg of thehomopolymer of monomer (a) (example 2) and of the homopolymer of thecomonomer TFE.

Example 9

Copolymer Monomer (a)/TFE 31/69 (Molar Ratio)

In a 5 lt autoclave, equipped with stirrer working at 630 rpm, therewere introduced, after evacuation, 3.5 lt of demineralized water and 35ml of microemulsion of perfluoropolyoxyalkylenes previously obtained asin example 1. The autoclave was then heated up to 70° C. and maintainedat said temperature for the whole reaction. The following mixture ofmonomers was then fed: tetrafuoroethylene (TFE) 70% by moles, monomer(a) 30% by moles, so as to bring the pressure up to 0.7 MPa. in theautoclave there were then introduced: 0.5 gr of ammonium persulphate(APS) as initiator; 3.29 gr of 1,4-diiodoperfluorobutane (C₄F₈I₂) aspolymer chain transfer agent; 1.5 gr of a bis-olefin of formulaCH₂═CH—(CF₂)₆—CH═CH₂; the addition of the bis-olefin was carried out in20 aliquots, each of 0.075 gr, starting from the beginning of thepolymerization and for every 5% increase in the monomer conversion. Thepressure of 0.7 MPa was maintained constant for the whole polymerizationby feeding a mixture formed by: tetrafuoroethylene (TFE) 60% by moles,monomer (a) 40% by moles. After 210 minutes of reaction, correspondingto 100% of the monomer conversion, the autoclave was cooled and thelatex discharged. The so obtained latex is coagulated with a solution ofaluminum sulphate (6 gr of Al₂(SO₄)₃ for each liter of latex) and driedat 90° C. in an air circulating over for 16 hours. 594 gr of polymer areobtained.

By ¹⁹F-NMR analysis of the polymer dissolved in hot C₆F₆ it was foundthat the molar percentage of monomer (a) in the polymer is 31.2%. TheT_(g), determined by DSC is −31.2° C. The Mooney viscosity (ML(1+10′ at121° C.)) determined according to the ASTM D 1646 method is 12 MU. Themechanical properties are shown in Table 1.

Example 10

Copolymer Monomer (a)/TFE 47/53 (Molar Ratio)

In a 5 lt autoclave, equipped with stirrer working at 630 rpm, therewere introduced, after evacuation, 3.5 lt of demineralized water and 35ml of microemulsion of perfluoropolyoxyalkylenes previously obtained asin example 1. The autoclave was then heated up to 70° C. and maintainedat said temperature for the whole reaction. The following mixture ofmonomers was then fed: tetrafuoroethylene (TFE) 38% by moles, monomer(a) 62% by moles, so as to bring the pressure up to 0.7 MPa. In theautoclave there were then introduced: 0.5 gr of ammonium persulphate(APS) as initiator; 3.29 gr of 1,4-diiodoperfluorobutane (C₄F₈I₂) aspolymer chain transfer agent; 1.5 gr of a bis-olefin of formulaCH₂═CH—(CF₂)₆—CH═CH₂; the addition of the bis-olefin was carried out in20 aliquots, each of 0.075 gr, starting from the beginning of thepolymerization and for every 5% increase in the monomer conversion. Thepressure of 0.7 MPa was maintained constant for the whole polymerizationby feeding a mixture formed by: tetrafuoroethylene (TFE) 60% by moles,monomer (a) 40% by moles. After 278 minutes of reaction, correspondingto 100% of the monomer conversion, the autoclave was cooled and thelatex discharged. The so obtained latex was coagulated as in example 9.574 gr of polymer were obtained.

By ¹⁹F-NMR analysis of the polymer dissolved in hot C₆F₆ it was foundthat the molar percentage of monomer (a) in the polymer is 47%. TheT_(g), determined by DSC, is −37.8° C. The Mooney viscosity (ML(1+10′ at121° C.)) determined according to the ASTM D 1646 method is 6 MU. Themechanical properties are shown in Table 1.

Example 11

Copolymer Monomer (a)/TFE 78/22 (Molar Ratio)

In a 5 lt autoclave, equipped with stirrer working at 630 rpm, therewere introduced, after evacuation, 3.5 lt of demineralized water and 35ml of microemulsion of perfluoropolyoxyalkylenes previously obtained asin example 1. The autoclave was then heated up to 60° C. and maintainedat said temperature for the whole reaction. The following mixture ofmonomers was then fed: tetrafuoroethylene (TFE) 20% by moles, monomer(a) 80% by moles, so as to bring the pressure up to 0.5 MPa. In theautoclave there were then introduced: 3.5 gr of ammonium persulphate(APS) as initiator; 1.24 gr of 1,4-diiodoperfluorobutane (C₄F₈I₂) aspolymer chain transfer agent; 0.5 gr of a bis-olefin of formulaCH₂—CH—(CF₂)₆—CH═CH₂; the addition of the bis-olefin was carried out in20 aliquots, each of 0.075 gr, starting from the beginning of thepolymerization and for every 5% increase in the monomer conversion. Thepressure of 0.5 MPa was maintained constant for the whole polymerizationby feeding a mixture formed by: tetrafuoroethylene (TFE) 22% by moles,monomer (a) 78% by moles. After 240 minutes of reaction, correspondingto 100% of the monomer conversion, the autoclave was cooled and thelatex discharged. The so obtained latex was coagulated as in example 9.130 gr of polymer were obtained.

By ¹⁹F-NMR analysis of the polymer dissolved in hot C₆F₆ it was foundthat the molar percentage of monomer (a) in the polymer is 85%. TheT_(g), determined by DSC, is −41.8° C. The Mooney viscosity (ML(1+10′ at121° C.)) determined according to the ASTM D 1646 method is 5 MU.

Example 12

Terpolymer Monomer (a)/TFE/MVE 22/68/10 (Molar Ratio)

In a 5 lt autoclave, equipped with stirrer working at 630 rpm, therewere introduced, after evacuation, 3.5 lt of demineralized water and 35ml of microemulsion of perfluoropolyoxyalkylenes previously obtained asin example 1. The autoclave was then heated up to 70° C. and maintainedat said temperature for the whole reaction. The following mixture ofmonomers was then fed: tetrafuoroethylene (TFE) 42% by moles, monomer(a) 31% by moles, methylvinylether (MVE) 27% by moles, so as to bringthe pressure up to 0.9 MPa. In the autoclave there were then introduced:0.75 gr of ammonium persulphate (APS) as initiator; 3.70 gr of1,4-diiodo perfluorobutane (C₄F₈I₂) as polymer chain transfer agent; 1.8gr of a bis-olefin of formula CH₂═CH—(CF₂)₆—CH═CH₂; the addition of thebis-olefin was carried out in 20 aliquots, each of 0.090 gr startingfrom the beginning of the polymerization and for every 5% increase inthe monomer conversion. The pressure of 0.9 MPa was maintained constantfor the whole polymerization by feeding a mixture formed by:tetrafuoroethylene (TFE) 59% by moles, monomer (a) 24% by moles,methylvinylether (MVE) 17% by moles. After 249 minutes of reaction,corresponding to 100% of the monomer conversion, the autoclave wascooled and the latex discharged.

The so obtained latex was coagulated as in example 9. 514 gr of polymerwere obtained.

By ¹⁹F-NMR analysis of the polymer dissolved in hot C₆F₆, it was foundthat the molar percentage of monomer (a) is 22.6%, of TFE is 67.6%, ofMVE is 9.8%. The T_(g), determined by DSC is −22.9° C. The Mooneyviscosity (ML(1+10′ at 121° C.)) determined according to the ASTM D 1646method is 29 MU. The mechanical properties are shown in Table 1.

Comments to Examples 9-12

The Applicant has unexpectedly found the versatility of monomer (a),shown in exs. 9-12, wherein the content of monomer (a) in the polymerranges from 22% to 78% moles. As comparison, MOVE 1 does not allow toprepare polymers having such a wide range of compositions.

TABLE 1 EXAMPLES 9 10 12 Formulation: Luperco 101 XL 45 phr 1.5 0.750.75 Drimix TALC 75% ″ 2 1 1 ZnO ″ 5 5 5 Black MT N990 15 15 15 Mooneypolymer ML_(121° (1 + 10)) 12 6 29 MDR 160° C., 12′ (ASTM D6204-97): MLLbf. in. 0.26 0.03 0.44 MH ″ 17.03 5.42 17.72 ts2 ″ 26 52 53 t′50 ″ 3558 75 t′90 ″ 67 122 180 Mechanical properties after post-cure at 230° C.for 1 + 4 h (ASTM D412-83) M100 Mpa 8.5 2.9 5.5 Stress at break ″ 11.65.1 9.9 Elong. at break % 123 151 130 Hardness Shore A 69 57 62Compression set 200° C. for 70 h O-ring (ASTM D 395) % 26 29 29 TR 10(ASTM D1329) ° C. −29 −36 −20 TR 70 (ASTM D1329) ° C. −14 −25 −10

1. Cured perfluoroelastomers comprising perfluoroelastomers curable byperoxidic route, said perfluoroelastomers comprising the monomer offormula (a) CF₃OCF₂OCF=CF₂, said perfluoroelastomers having a glasstransition temperature lower than −10° C., an improved combination ofmechanical and compression set properties at range of temperatures up to300° C., high thermal resistance, high molecular weight, and a —COF endgroup amount in the polymer lower than the sensitivity limit of thefollowing method: at the end of the polymerization, the polymer isisolated by coagulation by freezing and subsequent defrosting; it iswashed twice with demineralized water and is dried in a stove until aconstant weight; the —COF end groups are determined by FT-IRspectroscopy, wherein on a polymer film having a thickness from 50 to300 micron a scanning between 4,000 cm⁻¹ and 400 cm⁻¹ is initiallycarried out, the film being then kept for 12 hours in an environmentsaturated with ammonia vapours, and recording the IR spectrum under thesame conditions of the initial IR spectrum; elaborating the two spectraby subtracting to the signals of the spectrum related to the untreatedspecimen (initial spectrum) the corresponding signals of the specimenspectrum after exposure to ammonia vapours, drawing the differencespectrum, normalized by the following equation:$\frac{``{{Difference}\mspace{14mu}{spectrum}}"}{\left\lbrack {{film}\mspace{14mu}{weight}\mspace{14mu}{(g)/{film}}\mspace{14mu}{area}\mspace{14mu}\left( {cm}^{2} \right)} \right\rbrack};$the optical densities related to the —COF end groups, reacted with theammonia vapours, are measured; the optical densities are converted intommoles/kg of polymer by using the extinction coefficients reported inTable 1, page 73 of the report by M. Pianca et Al. “End groups influoropolymers”, J. Fluorine Chem. 95 (1999), 71-84; obtaining theconcentrations of the residual —COF end groups expressed as mmoles ofend groups —COF/Kg of polymer: in the perfluoroelastomer spectrum nobands related to COF groups (1900-1830 cm⁻¹) are detectable, the methodsensitivity limit being 0.05 mmoles/Kg.
 2. The cured perfluoroelastomersaccording to claim 1, wherein the curable perfluoroelastomers furthercomprise units deriving from bis-olefins of general formula:

wherein: R₁, R₂, R₃ , R₄, R₅, R₆, equal to or different from each other,are H or C₁-C₅, alkyls; Z is a C₁-C₁₈ linear or branched alkylene orcycloalkylene radical, optionally containing oxygen atoms, or a(per)fluoropolyoxyalkylene radical.
 3. The cured perfluoroelastomersaccording to claim 2, wherein the unit amount in the chain deriving fromthe bis-ole-fins of formula (I) is from 0.01 to 1.0% by moles per 100moles of the monomeric units, constituting the basic perfluoroelastomerstructure, the monomer total sum being 100%.
 4. The curedperfluoroelastomers according to claim 2, wherein in formula (I) Z is aC₄-C₁₂ perfluoroalkylene radical, while R₁, R₂, R₃, R₄, R₅, R₆ arehydrogen; when Z is a (per) fluoropolyoxyalkylene radical, it comprisesunits selected from the following: —CF₂CF₂O—, —CF₂CF(CF₃)O—, —CFX₁O—wherein X₁=F, CF₃, —CF₂CF₂CF₂O—, —CF₂—CH₂CH₂O—, —C₃F₆O—.
 5. The curedperfluoroelastomers according to claim 2, wherein Z has formula:-(Q)_(p)—CF₂O—(CF₂CF₂O)_(m)(CF₂O)_(n)—CF₂—(Q)_(p)-  (II) wherein: Q is aC₁-C₁₀ alkylene or oxyalkylene radical; p is 0 or 1; m and n are numberssuch that the m/n ratio is between 0.2 and 5 and the molecular weight ofsaid (per)fluoropolyoxyalkylene radical is in the range 500-10,000. 6.The cured perfluoroelastomers according to claim 5, wherein Q isselected from: —CH₂OCH₂—; —CH₂O(CH₂CH₂O)_(s)CH₂—, s being=1-3.
 7. Thecured perfluoroelastomers according to claim 2, wherein the bis-olefinhas formula:CH₂=CH—(CF₂)_(t0)—CH=CH₂ wherein t0 is an integer from 6 to
 10. 8. Thecured perfluoroelastomers according to claim 2, wherein the bis-olefinhas formula:CH₂=CH—(CF₂)₆—CH=CH₂  (b).
 9. The cured perfluoroelastomers according toclaim 1, wherein the curable perfluoroelastomers further comprise iodineand/or bromine in amounts between 0.001% and 5% by weight with respectto the total polymer weight.
 10. The cured perfluoroelastomers accordingto claim 9, wherein the iodine atoms are in the chain and/or in endposition.
 11. The cured perfluoroelastomers according to claim 9,wherein alternatively or in combination with iodine, bromine is present,both in the chain and in end position.
 12. The cured perfluoroelastomersaccording to claim 1, wherein the curable perfluoroelastomers furthercomprise in admixture a semicrystalline (per) fluoropolymer, in anamount in per cent by weight referred to the total of the dry weight ofthe mixture perfluoroelastomer+semicrystalline (per) fluoropolymer, from0% to 70%.
 13. The cured perfluoroelastomers according to claim 12,wherein the semicrystalline (per) fluoropolymer is formed oftetrafluoroethylene (TFE) homopolymers, or TFE copolymers with one ormore monomers containing at least one unsaturation of ethylene type, inan amount from 0.01% to 10% by moles, said comonomers having an ethyleneunsaturation both of hydrogenated and fluorinated type.
 14. The curedperfluoroelastomers according to claim 13, wherein the hydrogenatedcomonomers are selected from ethylene, propylene, acrylic monomers,styrene monomers.
 15. The cured perfluoroelastomers according to claim13, wherein the fluorinated comonomers are selected from the following:C₃-C₈, perfluoroolefins; C₂-C₈ hydrogenated fluoroolefins;perfluoroalkylethylene CH₂=CH—R_(f), wherein R_(f) is a C₁-C₆perfluoroalkyl; C₂-C₈ chloro- and/or bromo- and/or iodo-fluoroolefins;CF₂=CFOR_(f) (per) fluoroalkylvinylethers (PAVE), wherein R_(f) is aC₁-C₆ (per) fluoroalkyl; CF₂=CFOX (per) fluoro-oxyalkylvinylethers,wherein X is: a C₁-C₁₂ alkyl, or a C₁-C₁₂ oxyalkyl, or a C₁-C₁₂ (per)fluoro-oxyalkyl having one or more ether groups, or fluorodioxoles. 16.The cured perfluoroelastomers according to claim 12, wherein thecomonomers are PAVEs and fluorodioxoles.
 17. The curedperfluoroelastomers according to claim 1, wherein the curableperfluoroelastomers further comprise the following monomers (per cent bymoles): A) from 1% to 100%-of the monomer of formula:CF₂=CFOCF₂OCF₃  (a) B) from 0% to 99% of one or more perfluorinatedcomonomers having at least one unsaturation of ethylene type; the sum ofthe monomer molar percentages being 100%; with the proviso that if thecomonomer B) is TFE or the mixture of comonomers B) contains TFE, theTFE amount must be such that the polymer is elastomeric.
 18. The curedperfluoroelastomers according to claim 17, wherein when the copolymerdoes not contain other comonomers (B) besides TFE, the monomer amount offormula (a) is higher than about 15% by moles.
 19. The curedperfluoroelastomers according to claim 17, wherein comonomers B) areselected from the following: C₂-C₈ perfluoroolefins;perfluoroalkylvinylethers of formula CF₂=CFORf wherein Rf is a C₁-C₂perfluoroalkyl.
 20. The cured perfluoroelastomers according to claim 19,wherein the comonomer B) is tetrafluoroethylene (TEE) and/orperfluoromethylvinylether (MVE).
 21. The cured perfluoroelastomersaccording to claim 17, having the following monomer compositions,expressed in % by moles, the sum of the monomer molar percentages being100%: monomer of formula (a) 99.0%-99.99%, bis-olefin of formula (b)0.01-1%; monomer of formula (a): 15-40%, TFE: 60-85%, bis-olefin offormula (b) 0.01-1%; monomer of formula (a): 40-99%, TFE: 1-60%,bis-olefin of formula (b) 0.01-1%; monomer of formula (a) : 5-40%, MVE:5-30%, TFE: 50-85%, bis-olefin of formula (b) 0.01-1%; monomer offormula (a): 40-99%, MVE: 5-30%, TFE: 1-60%, bis-olefin of formula (b)0.01-1%.
 22. The cured perfluoroelastomers of claim 1, wherein thecurable perfluoroelastomers have a glass transition temperature lowerthan −20° C.
 23. The cured perfluoroelastomers of claim 2, wherein theC₁-C₁₈ linear or branched alkylene or cycloalkylene radical comprisesoxygen atoms.
 24. The cured perfluoroelastomers of claim 2, wherein theC₁-C₁₈ linear or branched alkylene or cycloalkylene radical is partiallyfluorinated.
 25. The cured perfluoroelastomers of claim 3, wherein theunit amount in the chain deriving from the bis-ole-fins of formula (I)is from 0.03 to 0.5% by moles of the monomeric units, constituting thebasic perfluoroelastomer structure, the monomer total sum being 100%.26. The cured perfluoroelastomers of claim 4, wherein in formula (I) Zis a C₄-C₈ perfluoroalkylene radical.
 27. The cured perfluoroelastomersof claim 5, wherein the molecular weight of said (per)fluoropolyoxyalkylene radical is in the range of 700 to 2,000.
 28. Thecured perfluoroelastomers of claim 9, wherein the curableperfluoroelastomers comprise iodine in amounts between 0.001% and 5% byweight with respect to the total polymer weight.
 29. The curedperfluoroelastomers of claim 12, wherein the curable perfluoroelastomerscomprise 0% to 50% by weight of the semicrystalline (per) fluoropolymer.30. The cured perfluoroelastomers of claim 13, wherein the amount oftetrafluoroethylene (TFE) homopolymers or TFE copolymers with one ormore monomers containing at least one unsaturation of ethylene type is0.05% to 7% by moles.
 31. The cured perfluoroelastomers according toclaim 15, wherein the C₁-C₁₂ (per) fluoro-oxyalkyl having one or moreether groups is perfluoro-2-propoxy-propyl.
 32. The curedperfluoroelastomers according to claim 15, wherein X is aperfluorodioxole.
 33. The cured perfluoroelastomers according to claim16, wherein the comonomers are PAVEs and perfluorodioxoles.
 34. Thecured perfluoroelastomers of claim 17, wherein the curableperfluoroelastomers comprise the following monomers (per cent by moles):A) from 5% to 100% of the monomer of formula:CF₂=CFOCF₂OCF₃  (a) B) from 0 to 95% of one or more perfluorinatedcomonomers having at least one unsaturation of ethylene type.
 35. Thecured perfluoroelastomers according to claim 19, wherein C₂-C₈perfluoroolefins include TFE and hexafluoropropene.
 36. The curedperfluoroelastomers according to claim 19, wherein Rf is —CF3.
 37. Thecured perfluoroelastomers according to claim 21, having the followingmonomer compositions, expressed in % by moles, the sum of the monomermolar percentages being 100%: monomer of formula (a): 99.0%-99.99%bis-olefin of formula (b) 1 %-0.01%; monomer of formula (a): 18-30%,TFE: 69-81.99%, bis-olefin of formula (b) 1-0.01%; monomer of formula(a): 39-98.99%, TFE 1-60%, bis-olefin of formula (b) 1-0.01%; monomer offormula (a): 5-40%, MVE: 5-30%, TFE: 50-85%, bis-olefin of formula (b)1-0.01%; monomer of formula (a): 40-99%, MVE: 5-30%, TFE: 1-60%,bis-olefin of formula (b) 1-0.01%.
 38. Manufactured articles comprisingthe cured perfluoroelastomers of claim
 1. 39. A method of manufacturingarticles, comprising using perfluoroelastomers curable by peroxidicroute, said perfluoroelastomers comprising the monomer of formula (a)CF₃OCF₂OCF=CF₂, said perfluoroelastomers having a glass transitiontemperature lower than −10° C., an improved combination of mechanicaland compression set properties at range of temperatures up to 300° C.,high thermal resistance, high molecular weight, and a —COF end groupamount in the polymer lower than the sensitivity limit of the followingmethod: at the end of the polymerization, the polymer is isolated bycoagulation by freezing and subsequent defrosting; it is washed twicewith demineralized water and is dried in a stove until a constantweight; the —COF end groups are determined by FT-IR spectroscopy,wherein on a polymer film having a thickness from 50 to 300 micron ascanning between 4,000 cm⁻¹ and 400 cm⁻¹ is initially carried out, thefilm being then kept for 12 hours in an environment saturated withammonia vapours, and recording the IR spectrum under the same conditionsof the initial IR spectrum; elaborating the two spectra by subtractingto the signals of the spectrum related to the untreated specimen(initial spectrum) the corresponding signals of the specimen spectrumafter exposure to ammonia vapours, drawing the difference spectrum,normalized by the following equation:$\frac{``{{Difference}\mspace{14mu}{spectrum}}"}{\left\lbrack {{film}\mspace{14mu}{weight}\mspace{14mu}{(g)/{film}}\mspace{14mu}{area}\mspace{14mu}\left( {cm}^{2} \right)} \right\rbrack};$the optical densities related to the —COF end groups, reacted with theammonia vapours, are measured; the optical densities are converted intommoles/kg of polymer by using the extinction coefficients reported inTable 1, page 73 of the report by M. Pianca et Al. “End groups influoropolymers”, J. Fluorine Chem. 95 (1999), 71-84; obtaining theconcentrations of the residual —COF end groups expressed as mmoles ofend groups —COF/Kg of polymer: in the perfluoroelastomer spectrum nobands related to COF groups (1900-1830 cm⁻¹) are detectable, the methodsensitivity limit being 0.05 mmoles/Kg.